Waiting for the first official D.C. freeze...

Closing in on longest freeze-free period on record

Percentage of years with the first freeze prior to and after today (11/19). 118 out of 138 years sampled saw a freeze today or earlier.

This has been a pretty pleasant November, though there have been periods of both well above and well below average temperatures. While a good portion of the area has seen a freeze at this point (i.e., Dulles as low as 28 on the 12th, with 12 lows in November at or below freezing), National Airport (DCA) still has not.

How odd is it that we have not seen it yet? Not that odd, actually. According to NOAA NOWData, the 1971-2000 average for first freeze in Washington is November 15. Keep in mind, this 30-year running normal will change once this year is complete, though the shift should not be major.

Keep on reading for more about climate norms for this time of year and also about another record held by 1980 that 2010 wants to challenge...

During the last decade, covering 2000-09, only two years saw a freeze before November 15, with the earliest on the 4th in 2006. The average date of D.C.'s first official freeze during this smaller, but more recent, period is closer to November 24th (or the Wednesday prior to Thanksgiving this year).

The earliest freeze on record at D.C. happened on October 10, 1895. All of the first eight occurrences on record were prior to 1909. The earliest freeze at DCA is October 20th, occurring in 1972 (31) and again in 1992 (32). The latest freeze on record at D.C. happened not too long ago, Dec. 22, 2001 (29). Of the nine times there has been no freeze at D.C. until December, eight are since 1975 and three happened during 2000-09.

Through (and including) today, there have been 265 freeze-free days at DCA since the last one on Feb. 27. In addition to being the earliest final freeze of a cold season, the Feb. 27 finish for winter 2009-10 freezes is the only time in recorded history that the last freeze has happened in February.

Length of time between the last freeze of the prior cold season and the first freeze of the new cold season during each calendar year going back to 1872. In the first, and most recent, available 30-year averages, the 1872-1901 period featured an average of 202.9 days between freezes while the 1980-2009 period averaged 234.9, a difference of about 1 month.

In the image above, the average time between freezes following the end of one cold season and the beginning of the next has been steadily growing in Washington over the course of the years on record. In a linear progression, one may have expected roughly 200 days to pass between the last and first freeze in the late 1800s. These days, it is past 230. Recent years in particular stand out as exceptions in the grand scheme, but perhaps it is more common on the smaller scale.

The 265 freeze-free days in D.C. this year so far puts 2010 in a position to soon climb out of 4th place all time in the category. The two spots right ahead of us are the 266 days in 1978 and 268 days in 2001. Now virtually guaranteed at least second all time, the only number left on the horizon is that of 1980. 275 freeze-free days were observed then.

It's interesting that climate change skeptics use the massive snowfall last winter as evidence that the planet is not warming, or undergoing climate change, yet this statistic, regarding the earliest last freeze date ever, has flown completely under the radar. And in terms of a freeze not occurring yet this year, yeah, perhaps it's not that odd, but that's only when considering the last 30 years. It certainly is odd when looking at the weather data over the last 100+ years.

hhhmmmmm.....days between last and first freeze... interesting. if one weren't predisposed not to, one could take this as yet more evidence for global warming....

i'm torn btwn rooting for yet another record this year, and rooting for snow next week/weekend.

along those lines, from the last thread, i said/asked:

yeah, yeah yeah... highs in the 50s/60s lows in the 30s/40s for the next 5/6 days.... booooring.

how are temps NEXT friday/weekend looking? or do i have to wait 'til the quasi-annual december 5/6 snowstorm?

the best i can gather from the NWS link on the upper left "at-a-glance" thing is 45 degrees at 8 pm on thursday the 25th - w/o ever having dropped below freezing - and the dew point stays lower than the temp, so...to my untrained eye that means no precip, white or otherwise, for thurdsay...

Centreville VA I still have roses that are squeezing out a few late November flowers.
Reminder: you can still plant spring flowering bulbs as long as the ground hasn't frozen. Just be prepared to battle the squirrels.

I am not a climate change skeptic. I believe it is occurring and that humans are to blame for at least a good part of it.

That said, I personally think this statistic has far more to do with the Urban Heat Island (UHI) effect than climate change in a broader sense.

As the area around DCA becomes increasingly urbanized, it holds heat better - and this is already a location that holds heat thanks to the river. I'd venture to guess that the vast majority of the metro area has seen a freeze, including many parts of DC proper. DCA's unique location in the center of the UHI, on the water, makes it particularly susceptible to high minimums.

This November reminds me of Nov. 2007. I've forgotten the high on Thanksgiving that year, but it was absurdly warm and until a cool front whipped through in the afternoon, there was still plenty of fall color around.

Fortunately, I spent a week in Munich and Zurich in mid-month and the snow and cold were great!

Are all of these data points for temperature taken at the same location? I thought I remember reading something here a long while ago about the temperature location moving for DCA. Might that shift this data a bit closer together and cause a decrease in the slope of the line?

dqreads, yes there was a shift in location in the early 1940s. That may play some factor but the trendlines are still basically the same. I'll take a closer look when I get home. I can't imagine that the temps at those two locations are that far off day-to-day anyway.

Having walked numerous times in the winter from the river (Kennedy Center) to 24th & L/M , where the weather bureau was formely located, my admittedly non-scientific observation is it's cooler and snowier in the winter even there, than right along the river. But looking at Ian's graph, the 1940s move to the airport doesn't seem to have had much impact on the long-range temperature trend.

It is fascintating to walk (or take the bus) from downtown or the Kennedy Center northwesward during snowfalls. There are definite and often-predictable "zones", e.g., west of Rock Creek Park, side streets off of Wisconsin Ave., etc. that get more snow.